Inhalation device

ABSTRACT

An inhalation device is provided by means of which material in powder form can be inhaled. The device comprises a body  55  defining a reservoir  56  for medicaments in powder form, an outlet  57  through which a user can inhale and a dosing member  53  with at least one metering recess  65  formed therein. The dosing member  53  is moveable between a position in which the at least one metering recess  65  communicates with the reservoir  56  to receive a dose of powder therefrom and a position in which the at least one metering recess  65  communicates with the outlet  57  to permit the user to inhale the dose. The at least one metering recess  65  is formed in a face of the dosing member  53 , the said face being mounted in contact against a similar mating face  60  of the body  55  at the lower end of the reservoir  56 . At least one moveable weight may be incorporated within the device, adapted to strike an anvil surface when the device is shaken.

This application is a continuation application of U.S. application Ser.No. 08/793,612 filed Jun. 17, 1997, now U.S. Pat. No. 6,065,471, whichis a 371 of PCT/EP95/03603 filed Sep. 13, 1995.

This invention relates to an inhalation device by means of which metereddoses of medicament in the form of a powder can be dispersed to a user.In particular it relates to a device of the type in which the medicamentpowder is held in bulk in a reservoir with which the device is provided,and is metered to the user from the reservoir.

In devices of the type just described, it is difficult to obtain doseswhich are equal to a nominal value to within the appropriate tolerance.It will be understood that the tolerance permitted is often very small,as it is important that the user should be given a dose which is veryclose to the nominal value. In order to maintain the medicament powderin a manageable state it needs to be kept dry. Any ingress of moistureinto the reservoir from outside can cause the medicament powder toagglomerate and this may be detrimental to its free flowing propertiesrendering it difficult to meter consistent doses from the reservoir. Inthe absence of adequate reservoir sealing it may be necessary toincorporate a desiccant cartridge into the reservoir to absorb anymoisture that does enter. This is often insufficient to preventdeterioration of the medicament powder.

It is an object of the present invention to provide a device of the typejust described, in which doses can be repeatedly accurately dispersed,without requiring a dispensing mechanism of undue complexity.

It is a further object of the present invention to provide a device ofthe type just described, but which additionally incorporates a simpleand efficient sealing means to prevent ingress of moisture into thereservoir.

According to the present invention there is provided an inhalationdevice comprising a body defining a reservoir for medicament in the formof a powder, an outlet through which a user can inhale, and a dosingmember with at least one metering recess formed therein, the dosingmember being moveable between a first position in which the at least onemetering recess communicates with the reservoir to receive a dose ofpowder therefrom and a second position in which the at least onemetering recess communicates with the outlet to permit the user toinhale the dose, the at least one metering recess being formed in a faceof the dosing member, the said face being mounted in contact against asimilar mating face of the body at the lower end of the reservoir, andat least one moveable weight adapted, when the device is shaken, tostrike an anvil surface defined in the device.

The at least one weight may be slidable longitudinally of the device ina respective bore, with the anvil surface being at the lower end of thebore.

Alternatively the weight may be in the form of a ring encircling thedevice and slidable longitudinally thereof.

According to a further aspect of the invention the face of the dosingmember and the mating face of the body are sealing faces with highlypolished smooth surfaces which form a sliding seal which excludessubstantially all air from the interface therebetween.

Suitably the sealing faces have a surface texture sufficiently smooth tohave a roughness average value (Ra) of 0.5 microns or less, preferably0.2 microns or less.

Suitably the sealing faces are flat. More suitably they have a flatnessof 0.005 mm or less, preferably 0.003 mm or less.

Alternatively the sealing faces may be frusto-conical. The sealing facesmay alternatively be cylindrical. In a further alternative the sealingfaces may be spherical.

The sealing surfaces are suitably made of a hard rigid material such asacetal resins, ceramics or metals.

A further aspect of the invention provides an inhalation devicecomprising a reservoir for medicament in the form of a powder, an outletthrough which a user can inhale, a metering means adapted to communicatewith the reservoir to receive a dose of powder therefrom and with theoutlet to permit the user to inhale the dose, and at least one weightmoveable in the device and adapted, when the device is shaken, to strikean anvil surface defined in the device.

Additionally the invention provides an inhalation device comprising abody forming a reservoir for medicaments in the form of a powder, anoutlet through which a user can inhale, and a dosing member with atleast one metering recess formed therein, the dosing member beingmoveable between a position in which the at least one metering recesscommunicates with the reservoir to receive a dose of powder therefromand a position in which the at least one metering recess communicateswith the outlet to permit the user to inhale the dose, the at least onemetering recess being formed in a face of the dosing member, the saidface being mounted in contact against a similar mating face of the body,characterised in that the said face of the dosing member and the saidmating face of the body have highly polished smooth surfaces which forma contacting face to face kinetic seal which excludes substantially allair from the interface. The term ‘kinetic seal’ in this context means aseal that can withstand relative movement of the two faces.

Another embodiment of the invention provides an inhalation devicecomprising a body defining a reservoir for medicament in the form of apowder, an outlet through which a user can inhale, and a dosing memberwith at least one metering recess formed therein, the dosing memberbeing moveable between a first position in which the at least onemetering recess communicates with the reservoir to receive a dose ofpowder therefrom and a second position in which the at least onemetering recess communicates with the outlet to permit the user toinhale the dose, the at least one metering recess being formed in a faceof the dosing member, the said face being mounted in contact against asimilar mating face of the body at the lower end of the reservoir,characterised in that the said face of the dosing member and the saidmating face of the body are sealing faces with highly polished surfaceswhich form a sliding seal which excludes substantially all air from theinterface therebetween.

The invention is further described below with reference to theaccompanying drawings in which:

FIG. 1 is a perspective view of an embodiment of a device according tothe invention, showing the main body components in disassembled form;

FIG. 2 is an underplan view of the body of the device of FIG. 1;

FIG. 3 is a rear view of the body, partly cut away;

FIG. 4 is a section on line 4—4 in FIG. 2;

FIG. 5 is a plan view of the body;

FIG. 6 is a perspective view of a guide insert which is located insidethe reservoir defined in the body;

FIG. 7 is a plan view, partly cut away and on a larger scale, of adosing member which forms part of the device of FIG. 1;

FIG. 8 is a partial section on line 8—8 in FIG. 7;

FIG. 9 shows a spring-retaining element which is inserted in the dosingmember;

FIG. 10 is a side elevation of the dosing member of FIGS. 7 and 8;

FIG. 11 is a section through a second embodiment of a device accordingto the invention;

FIG. 12 is a section on line 12—12 in FIG. 11; and

FIGS. 13 to 15 are perspective views showing three steps in theoperation of the devices according to FIGS. 11, 12 and 16 to 19.

FIG. 16 is a section through a third embodiment of a device according tothe invention.

FIG. 17 is a section on line 17—17 in FIG. 16;

FIG. 18 is an exploded view of the embodiment shown in FIGS. 16 and 17;and

FIG. 19 is an exploded perspective view, partly cut away, showing thedose indicator mechanism of the embodiment shown in FIGS. 16 to 18,

As shown in FIG. 1, the device comprises a body 1, a cover 2, a dosingmember 3 and a nut 4. The body 1 has a elongate main body portion 5which defines a reservoir 6. The body may be moulded from polycarbonate,aluminium or any other rigid material which will transmit vibrations.The reservoir 6 contains a supply of medicament in the form of a powder.As is common in powder inhaler devices of this type, the reservoir 6 maycontain an overfill of powder to ensure that there is sufficient powderin the reservoir to deliver the correct dosage of powder for each of theprescribed number of doses for the powder supply contained. Thus, whilstthe device may be provided with a prescribed life of 200 doses ofpowder, the reservoir may contain the equivalent of 240 doses of powder.The reservoir 6 may also be provided with a window (not shown) to allowthe user to check whether there is sufficient powder remaining.

The medicament is one which is suitable for inhalation, and many suchmedicaments are well known to those skilled in the art, for example forthe treatment of asthma. Powdered medicaments suitable for this purposeinclude salbutamol, beclomethasone, salmeterol, fluticasone, formoterol,terbutaline, budesonide and flunisolide, and physiologically acceptablesalts, solvates and esters or any combination thereof. Preferredmedicaments are salbutamol, salbutamol sulphate, salmeterol, salmeterolxinafoate, fluticasone propionate, beclomethasone dipropionate andterbutaline sulphate. Individual isomers, such as R-salbutamol, can alsobe used. It is to be understood that the medicament powder may consistpurely of one or more active ingredients, or there may additionally be acarrier, for example lactose powder.

The upper end of the reservoir is closed by the cover 2 which may, forexample, be provided with a desiccant cartridge (not shown) to absorbmoisture and reduce the risk of the powder in the reservoir absorbingmoisture and undergoing agglomeration of the particles thereof. Thecover 2 may be removably secured to the body 1 by any known means, forexample by means of a screw thread or a snap fit, to enable refilling ofthe reservoir 6 with powder. In this case a pharmaceutical grade rubbersealing ring (not shown) may be incorporated between the cover 2 andbody 1 to prevent ingression of moisture into the reservoir 6.Alternatively, the device may be intended to be disposable afterexhaustion of the supply of powder in the reservoir, in which case thecover 2 may be permanently secured to the body 1 by use of an adhesive,ultrasonic welding or any other method. It is to be understood that themedicament powder may consist purely of one or more active ingredients,or there may additionally be a carrier, for example lactose powder.

Extending laterally from the lower end of the main body portion 5 is anoutlet 7, which, in the embodiment illustrated in FIG. 1 is in the formof a mouthpiece. If, however, the device were intended for nasalinhalation this would be replaced by a nosepiece. At its radially innerend the interior of the mouthpiece has a downwardly opening aperture 8which communicates, as described below, with a dosing chamber containinga dose of powder to be inhaled. The outlet 7 is also provided with apair of air inlets 9, one on each side, which allow the user to inhaleadditional air, and reduce the resistance to inhalation which the userexperiences. It is understood that more air inlets could be provided onoutlet 7 to allow more air into the outlet and to vary the air flowcharacteristics.

The main body portion 5 has a base 10 in which is provided an arcuateaperture 11 through which powder can pass from the reservoir to thedosing member 3. The aperture 11 is surrounded by a wall 11 a whichextends downwardly from the base 10. Powder is guided to the aperture 11by a guide insert 12, which is illustrated in FIG. 6. The guide insert12 also serves to close off the reservoir from the interior of theoutlet 7, so that powder cannot pass directly from the reservoir to theoutlet.

A shaft 13, integral with the base 10 or fixedly secured thereto,extends downwardly therefrom. The shaft has a first portion 14 of largerdiameter in which is formed a longitudinally extending slot 15, and asecond portion 16 which is of smaller diameter and has a screwthreadedexternal surface. The base 10 is further provided with two lugs 30arranged approximately equidistantly from one another and from thecentre of the aperture 11, which extend downwardly from the base by anamount equal to the height of the wall 11 a surrounding the aperture 11.The lugs 30 and wall 11 a together define a planar surface forengagement by the upper surface of the dosing member 3.

The wall of the main body portion 5 of the body 1 is of sufficientthickness, at least in certain regions, to permit two longitudinal bores18 to be formed therein. It is to be understood that instead of twobores, a single bore, or more than two bores, for example three bores,may be provided. An elongate weight 17 is slidably received in each ofthe bores. The weight is of a dense material, preferably metal, and onesuitable material is stainless steel. An anvil 19 may be fixedly securedin the lower end of each bore. This is also preferably of metal, andbrass has been found to be a suitable material. The upper end of eachbore has a screwthreaded portion 20, which can receive a screw (notshown) used to secure the cover 2 to the body 1.

The dosing member 3 has an upper surface 21 in which is formed ametering recess 22. This has a volume equal to the volume of one dose ofthe powder in the reservoir. As seen in plan view, the recess 22 has ashape which is congruent to the aperture 11 in the base of the main bodyportion. As seen in section in FIG. 8, the recess has the form ofshallow, arcuate depression with gently sloping sides. The advantages ofthis shape of recess will be explained below. It has been found that arecess capacity of between 5 mg and 26 mg of powder may be effectivelyemployed. As shown in FIG. 7, the dosing member 3 has a nearly radialbore 23 in which a ratchet pawl 24 is slidably received. The pawl isurged inwardly by a spring 25 which is held in compression by aretaining element 26 received in a dovetail-shaped recess 27 in theperiphery of the member 3. The inner end of the pawl 24 is urged againstthe portion 14 of the shaft 13. When the member 3 is in one particularposition the pawl engages in the slot 15 in the portion 14. This is theposition which is required during inhalation, as will be explainedfurther below.

The dosing member 3 has a central opening 28 of stepped diameter,corresponding to the diameters of the portions 14 and 16 of the shaft13, and is retained on the shaft by the nut 4 which engages the threadedsurface of the shaft portion 16. A pharmaceutical grade rubber sealingring or washer (not shown) may be incorporated in a groove aroundaperture 11 to prevent ingress of moisture between the body 1 and dosingmember 3 into the reservoir 6. Such a sealing ring or washer may have alow friction coating such as polytetrafluoroethylene. The dosing member3 has an indicator arrow 29 in its peripheral surface, and correspondingmarks (not shown) are provided on the surface of the body 1, with whichthe user aligns the arrow at the various stages of operation of thedevice.

In operation, the user initially rotates the dosing member to theposition in which the dosing recess is directly below the aperture 11,and thus in communication with the reservoir 6. The user then shakes thedevice in a generally upward and downward motion, while maintaining thedevice in a generally upright orientation. The weights 17 are therebycaused to travel up and down their respective bores 18. In so doing, theweights repeatedly strike against the anvils 19. The jolts which thisproduces cause the powder in the reservoir to be urged downwardly, andpowder thus enters the metering recess 22. The jolts also have theeffects of eliminating any bridging of powder, and ensuring that thepowder is packed to a constant density. The latter point is important inensuring uniform doses. What is desired is a uniform weight of powder,and the metering recess will not provide this unless the powder is ofconstant density. The shape of the metering recess 22 will have a directeffect on its filling characteristics. A shallow, arcuate depressionwill provide for rapid and complete filling of the recess with powderfrom the reservoir at substantially constant density throughout therecess.

The user then rotates the dosing member 3 through 180° to bring therecess 22 into alignment with the aperture 8 at the radially inner endof the outlet 7. The user knows when this position has been reached, asthe pawl 24 is felt to engage with the slot 15. The user then inhalesthrough the outlet 7, causing air to enter the outlet through the airinlets 9. The turbulent air flow created by the user inhaling throughthe outlet causes the powder in the recess 22 to be entrained in theairflow and inhaled by the patient. The shallow arcuate shape of therecess 22 allows for efficient entrainment of powder in the air flow.After inhalation, the user returns the dosing member to its initialposition, ready for use again when required.

It will be appreciated by one skilled in the art that the size, numberand configuration of the weights 17 in the device may be varied toprovide optimum performance of the device depending on the size of thereservoir 6, the material from which the body 1 is moulded, its capacityto transmit vibrations, and the characteristics of the powder in thereservoir. For example, it has been found that positioning the bores 18within the reservoir provides improved recess powder fillingperformance.

An alternative embodiment of the invention is shown in FIGS. 11 to 15.As in the embodiment shown in FIGS. 1 to 10, the embodiment of thedevice shown in cross section in FIGS. 11 and 12 comprises a main bodyportion 5 which defines a reservoir 6 and a reservoir cover or end cap2. The reservoir 6 contains a supply of medicament in the form of apowder (not shown). The medicament may be as described above withreference to the embodiment shown in FIGS. 1 to 10.

The reservoir cover 2 may be provided with a desiccant cartridge (notshown) to absorb moisture and reduce the risk of the powder in thereservoir absorbing moisture and undergoing agglomeration of theparticles thereof. The cover 2 may be removably secured to the body 5 byany known means, for example by means of a screw thread or a snap fit,to enable refilling of the reservoir 6 with powder. In this case apharmaceutical grade rubber sealing ring 4 may be incorporated betweenthe cover 2 and body 5 to prevent ingression of moisture into thereservoir 6. Alternatively, the device may be intended to be disposableafter exhaustion of the supply of powder in the reservoir, in which casethe cover 2 may be permanently secured to the body 5 by use of anadhesive, ultrasonic welding or any other method.

At its lower end the main body portion 5 is fitted with a base 10 whichtogether with body 5 defines an aperture 11 which is offset from thevertical axis of the device and through which powder can pass from thereservoir to the dosing member 3. Powder is guided to the aperture bythe walls of the reservoir which form a hopper. Extending laterally fromthe lower end of main body 5 is mouthpiece 7. If, however, the devicewere intended for nasal inhalation this would be replaced by anosepiece. Dosing member 3 is mounted upon lower body portion 9 which ispivotally connected to main body 5 such that it may rotate about thevertical axis of the device. As explained in more detail below, lowerbody portion 9 serves to allow rotation of the dosing member 3 whilstmaintaining the same in axial alignment with base 10. It also urges thedosing member 3 into close contact with base 10. Dust cover 33 isattached to lower body portion 9 through pivot 34.

A weight 31 in the form of a ring encircles the reservoir 6 and isslidable longitudinally thereof. The locus of movement of the weight 31is defined towards the top of the reservoir by an end stop 32 formed asan integral part of the body 5, and towards the bottom of the reservoirby base 10 which behaves as an anvil. It is to be understood that whilstthe device described herein incorporates a weight for the purposedescribed below, the weight is not an essential element of the inventionand it might be chosen to omit the incorporation of the weight.

The lower face of base 10 is provided with a highly polished smooth andflat surface as is the contacting upper face of dosing member 3. Thesesurfaces are ground and polished to render a surface finish giving aflatness which does not undulate over its area by more than 0.003 mm anda surface texture having a roughness average value (Ra) of 0.2 micronsas internationally designated under ISO/R468, meaning that the averageheight of the irregularities constituting surface texture is 0.2microns. These highly polished flat faces provide contacting surfacesbetween which there is substantially no clearance. It has been foundthat by providing such highly polished flat faces, the faces adhere toeach other yet slide over each other as they are wrung together duringassembly and use in the same way as mechanical slip gauges adhere toeach other when wrung together. Air and powder are thus excluded fromthe interface between the base 10 and dosing member 3. When assembledthe faces adhere firmly together but may be slid over each other withoutaffecting the closeness of the interfacial contact. Such contactingsurfaces have been found to provide excellent sealing characteristicsboth in the static state and during the sliding motion of one face overthe other preventing both loss of powder from and ingression of moistureinto the reservoir 6 through the interface between the base 10 anddosing member 3. This type of kinetic or sliding seal obviates the needfor any additional sealing means between base 10 and dosing member 3.The contacting surfaces of base 10 and dosing member 3 are made of ahard rigid material, and suitable materials include acetal resins,ceramics and metals.

In the embodiment described, the two faces are formed by the surfaces offlat discs. It will be appreciated that disc shapes are not essential.Contact faces may be formed by the surfaces of a frusto-cone and acorrespondingly frusto conical socket, by the contacting surfaces of twoco-axial cylinders or by two correspondingly partially sphericalcontacting ball and socket surfaces.

In operation, the user initially shakes the device in a generally upwardand downward motion while maintaining the device in a generally uprightorientation as shown in FIG. 13. Weight 31 is thereby caused to travelup and down the reservoir, so repeatedly striking end stop 32 and base10. The jolts which this produces causes the powder in the reservoir tobe urged downwardly and to enter the metering recess 22.

The user then opens dust cover 33, as shown in FIG. 14, and rotates thecover which is connected to lower body portion 9 as described above,through 90° as shown in FIG. 5, to move the dust cover 33 away from themouthpiece 7 to allow access thereto and to bring the recess 22 intoalignment with the aperture 8 leading to the mouthpiece 7 The user knowswhen this position has been reached as the lower body portion 9 engagesa stop (not shown) and will not move any further. The user then inhalesthrough mouthpiece 7. After inhalation the user returns the lower bodyportion 9 to its initial position and closes the dust cover 33.

In the device shown in FIGS. 11 and 12 the aperture 11 is radiallyoffset by an angle of 90° about the vertical axis of the device from theaperture 8 at the inner end of the mouthpiece to allow the dust coverand lower body portion 9 to be moved through 90° for ease of access tothe mouthpiece. However, it will be appreciated that this angle can besubstantially increased or slightly decreased according to the desiredangle of rotation of the dust cover, lower body portion and dosingmember.

Further possible modifications to the device described includeincorporation of a suitable dose counting mechanism to give the user anindication of the amount of powder remaining in the device.

A further embodiment of the invention is shown in FIGS. 16 to 19. As inthe previous embodiments, the device shown in cross section in FIGS. 16and 17 and in exploded view in FIG. 18 comprises an elongate main bodyportion 55 which defines a reservoir 56 and a reservoir cover or end cap52. The reservoir 56 contains a supply of medicament in the form of apowder (not shown). The reservoir cover 52 is secured to the body 55 bya snap fit and a pharmaceutical grade rubber sealing ring 54 isincorporated between the cover 52 and body 55 to prevent ingression ofmoisture into the reservoir 56.

At its lower end the main body portion 55 is fitted with a base member60 which together with body 55 defines an aperture 51 which is offsetfrom the vertical axis of the device and through which powder can passfrom the reservoir to a recess 65 in dosing member 53. The lower face ofbase member 60 is provided with a similarly highly polished smooth andflat surface to that described with reference to the embodiment shown inFIGS. 11 to 15 as is the upper face of dosing member 53. Powder isguided to the aperture by the walls of the reservoir which form ahopper. Extending laterally from the lower end of the main body 55 ismouthpiece 57. Dosing member 53 is mounted upon lower body assembly 59which is pivotally connected to main body 55 such that it may rotateabout the vertical axis of the device. Lower body assembly 59 serves totransmit rotational movement thereof to the dosing member 53 whilstmaintaining the same in axial alignment with base member 60. It alsourges dosing member 53 into close contact with base 60 by means ofspring 61. Dust cover 63 (not shown in FIGS. 16 and 17) is attached tolower body portion 69 through pivot 64.

The wall of the main body 55 is provided with three longitudinal bores58 substantially equidistantly spaced around the reservoir 56. Acylindrical weight 67 is slideably received in each of the bores 58. Theweights 67 may be made of a rust resistant metal such as stainless steelor other hard material such as acetal resin. The bores are each blind attheir upper ends and closed by a pressed-in stainless steel ball bearing68 at their lower ends which also act as anvils against which weights 67may impact as described later.

A dose indicator drive means comprising a shaft 70 provided with a screwthread over much of its length, a sprung lug 71 at the base of thethread and a sprocket 72 with inclined teeth positioned below the lug isrotatably mounted within a bore 73 in the wall of the main body 55 (seeFIG. 19). An indicator nut 77 is threaded into the shaft with aprojection protruding through an indicator window 74 in the wall of bore73 which prevents the indicator nut 77 from rotating with shaft 70.Sprung lug 71 engages with teeth 75 formed within bore 73 to form aratchet allowing shaft 70 to rotate in one direction only. Sprocket 72is located adjacent the periphery of dosing member 53 which is providedwith a second sprung lug 76.

Operation of the device is similar to that described with reference tothe embodiment shown in FIGS. 11 to 15. The user initially shakes thedevice in a generally upward and downward motion while maintaining thedevice in a generally upright orientation as shown in FIG. 13. Weights67 are thereby caused to travel up and down bores 58 next to thereservoir, so repeatedly striking anvils 68. The vibrations which thisproduces are transmitted through base member 60 and body 55 to thepowder in the reservoir, and this encourages powder to flow downwardlyand enter metering recess 65 within dosing member 53.

The user then opens dust cover 63, as shown in FIG. 14, and rotates thecover which is connected to lower body assembly 59 as described abovethrough 90° as shown in FIG. 5, to move dust cover 63 away frommouthpiece 57 to allow access thereto and to bring recess 65 intoalignment with the aperture at 66 leading to the mouthpiece 57. As thedosing member 53 rotates with the lower body assembly 59, lug 76 engagesan inclined tooth presented by sprocket 72 of the dose indicator drivemeans. The dose indicator drive means is prevented from turning in thedirection urged by lug 76 by virtue of the ratchet mechanism formed byteeth 75 and lug 71. As a result, lug 76 rides over the inclined toothand out of engagement with sprocket 72. The lower body assembly 59engages a stop (not shown) and will not move any further when the recess65 is correctly aligned with aperture 66.

The user now inhales through mouthpiece 57. Air is drawn through grill80 and passage 81, defined by body 55 and hole 82 in base member 60, andentrains the powder in recess 65 of dosing member 53. The airflow drawsthe entrained powder through the mouthpiece 57 and is inhaled by theuser. Further air is drawn into the mouthpiece through holes 82 oneither side of mouthpiece 57 and this creates turbulence which helps tobreak-up any agglomerates of powder entrained.

After inhalation the user returns lower body assembly 59 to its initialposition and closes the dust cover 63. As dosing member 53 rotates, lug76 again engages sprocket 72 of the dose indicator drive means. As theratchet mechanism formed by teeth 75 and lug 71 allows movement of thedose indicator drive means in the direction as now urged by lug 76, thedose indicator drive means is rotated by one tooth pitch throughengagement with lug 76 as it passes sprocket 72. Rotation of the doseindicatior drive means causes the captive dose indictor nut 73 to traveldown threaded shaft 70. The pitch of the thread and the number of teethon sprocket 72 are selected to ensure that the dose indicator nuttravels from the uppermost “full” position to the lowermost “empty”position when the device has been used sufficiently to deliver itsprescribed number of doses, so indicting to the user that the device isempty.

It will be understood that the present disclosure is for the purpose ofillustration only and the invention extends to modifications, variationsand improvements thereto.

What is clamed is:
 1. An inhalation device comprising a body forming areservoir for medicaments in the form of a powder, an outlet throughwhich a user can inhale, and a dosing member with at least one meteringrecess formed therein, the dosing member being movable between aposition in which the at least one metering recess communicates with thereservoir to receive a dose of powder therefrom and a position in whichthe at least one metering recess communicates with the outlet to permitthe user to inhale the dose, the at least one metering recess beingformed in a face of the dosing member, the face being mounted in contactagainst a similar mating face of the body, characterised in that theface of the dosing member and the said mating face of the body havehighly polished smooth surfaces which form a contacting face to faceseal in which said sealing faces adhere to each other sufficiently toexclude air and moisture while being slidable relative to each other. 2.A device according to claim 1, characterised in that the sealing faceshave a surface texture sufficiently smooth to have a roughness averagevalue (Ra) of 0.5 microns or less.
 3. A device according to claim 2,characterised in that the sealing faces have a surface texturesufficiently smooth to have an Ra value of 0.2 microns or less.
 4. Adevice according to claim 1, characterised in that the sealing faces areflat.
 5. A device according to claim 4, characterised in that thesealing faces have a flatness of 0.005 mm or less.
 6. A device accordingto claim 5, characterised in that the sealing faces have a flatness of0.003 mm or less.
 7. A device according to claim 1, characterised inthat the sealing faces are cylindrical.
 8. A device according to claim1, characterised in that the sealing faces are disc shaped.
 9. A deviceaccording to claim 1, characterised in that the sealing faces are madeof a hard rigid material.
 10. A device according to claim 9,characterised in that the sealing faces are made of acetal resin.
 11. Adevice according to claim 9, characterised in that the sealing faces aremade of ceramics.
 12. A device according to claim 9, characterised inthat the sealing faces are made of metal.
 13. A device according toclaim 1, further comprising a dose indicating means adapted to displayto a user the quantity of medicament remaining within the reservoir. 14.A device according to claim 1, characterised in that the sealing facesare highly polished surfaces made of a hard rigid material.
 15. A deviceaccording to claim 1, characterised in that the sealing faces are highlypolished metal surfaces.
 16. An inhalation device comprising a bodydefining a reservoir for medicaments in the form of a powder, an outletthrough which a user can inhale and a dosing member with at least onemetering recess formed therein, the dosing member being movable betweena position in which the at least one metering recess communicates withthe reservoir to receive a dose of powder therefrom and a position inwhich the at least one metering recess communicates with the outlet topermit the user to inhale the dose, the at least one metering recessbeing formed in a face of the dosing member, the face being mounted incontact against a similar mating face of the body at the lower end ofthe reservoir, characterised in that the face of the dosing member andthe mating face of the body are sealing faces with highly polishedsurfaces which adhere to each other sufficiently to exclude air andmoisture while being slidable relative to each other.
 17. A deviceaccording to claim 16, characterised in that the sealing faces have asurface texture sufficiently smooth to have a roughness average value(Ra) of 0.5 microns or less.
 18. A device according to claim 17,characterised in that the sealing faces have a surface texturesufficiently smooth to have an Ra value of 0.2 microns or less.
 19. Adevice according to claim 16, characterised in that the sealing facesare flat.
 20. A device according to claim 19, characterised in that thesealing faces have a flatness of 0.005 mm or less.
 21. A deviceaccording to claim 20, characterised in that the sealing faces have aflatness of 0.003 mm or less.
 22. A device according to claim 16,characterised in that the sealing faces are cylindrical.
 23. A deviceaccording to claim 16, characterised in that the sealing faces are discshaped.
 24. A device according to claim 16, characterised in that thesealing faces are made of a hard rigid material.
 25. A device accordingto claim 24, characterised in that the sealing faces are made of acetalresin.
 26. A device according to claim 24, characterised in that thesealing faces are made of ceramics.
 27. A device according to claim 24,characterised in that the sealing faces are made of metal.
 28. A deviceaccording to claim 16, further comprising a dose indicating meansadapted to display to a user the quantity of medicament remaining withinthe reservoir.
 29. A device according to claim 16, characterised in thatthe sealing faces are highly polished surfaces made of a hard rigidmaterial.
 30. A device according to claim 16, characterised in that thesealing faces are highly polished metal surfaces.